我有一个MySQL数据库，里面有3个表。
配置文件，p_ tags，标签
数据库：
profile
pid | name
ptags
ptid | pid | tagid
tags
tagid | tag
DB看起来像这个
profile
pid | name
1 Randy
2 Jeff
3 Mike
ptags
ptid | pid | tagid
1 1 1
2 1 2
3 2 1
4 2 3
5 3 1
6 3 2
7 3 3
tags
tagid | tag
1 science
2 filosophy
3 hydrology
我需要的是创建一个查询，显示配置文件中具有共享标签的名称和总共享标签
即
Results
Name | Name2 | Count
Randy - Jeff - 1
Randy - Mike - 2
Jeff - Randy - 1
Jeff - Mike - 2
Mike - Randy - 2
Mike - Jeff - 2
等等。
我不知道我解释对不对。
我读
https://www.simple-talk.com/sql/t-sql-programming/divided-we-stand-the-sql-of-relational-division/
来自另一个类似于这篇文章的链接，但我无法理解：）。
SQLFiddle：http://sqlfiddle.com/#！9/42bde6
在查询中使用join:
SELECT p1.name Name1, p2.name Name2, Count(tagid)
FROM ptags AS t1
INNER JOIN ptags AS t2 ON t2.tagid = t1.tagid and t2.ptid <> t1.ptid
INNER JOIN profile AS p1 ON p1.pid = t1.pid
INNER JOIN profile AS p2 ON p2.pid = t2.pid
GROUP BY p1.name, p2.name
如果你只需要一行的名字对，那么试试这个：
SELECT p1.firstname Name1, p2.firstname Name2, Count(t1.tagid)
FROM profile_hashtags AS t1
INNER JOIN profile_hashtags AS t2
ON t2.tagid = t1.tagid and t2.pHid > t1.pHid
INNER JOIN `profile` AS p1 ON p1.pid = t1.pid
INNER JOIN `profile` AS p2 ON p2.pid = t2.pid
GROUP BY p1.firstname, p2.firstname;